Aëroplane flying, in a large measure, is a knack, and must be acquired. The air pressure never touches the machine in exactly the same point for two consecutive seconds, and, because of this, the centre of gravity is constantly changing. Centre of gravity and centre of air pressure must coincide at all times if the machine is to be kept in the air, and the success or failure to do this proves the competency or the incompetency of the operator.
The Traquair aëroplane—upon which model Matt's machine had been built—preserved its equilibrium while aloft by an elongation, or contraction, of the wing tips. A lever regulated this; and, whenever Matt was flying, the lever was moving continuously, the ends of the wings darting out and in with lightning-like rapidity, one side presenting greater wing area to the pressure while the other presented less, and vice versa.
Motor Matt's engagement with Boss Burton did not cover long flights. Usually, if the weather was propitious, he made it a point to remain aloft about fifteen minutes, circling about the show grounds, turning sharp corners and cutting airy "figure eights," in order to show the capabilities of the aëroplane.
"Get your trapeze over, Le Bon!" he called, while they were steadily mounting.
A laugh was his answer—a silvery ripple of a laugh that had a familiar ring in his ears and now filled him with consternation. He dared not look around.
"Haidee!" he exclaimed.
"Are you mad at me, Motor Matt?" came the voice of the girl.
She cautiously slipped into the seat beside him, her heightened color and sparkling eyes showing her excitement.
"This was a trick," went on Matt calmly, attending to his work with an indifference more apparent than real, "which you and Le Bon and Burton played on me?"
"It was Burton's idea, and he told it to me while we were going after Archie le Bon. Archie was to pretend to run with the machine, and I was to be with him. When the machine got to going too fast for us, Archie was to drop to one side and I was to spring to the lower wing. Your back would be in my direction, and you couldn't see me."